Pages 271-275, 277 Flashcards
Multiple allelism
the existence of more than two alleles of the same gene.
Polymorphic
when more than two distinct phenotypes are present in a population owing to multiple allelism.
Codominance
the simultaneous expression of the phenotype associated with each allele in a heterozygote.
Incomplete dominance
heterozygotes have a phenotype that is between the two different homozygous parents.
Three possible dominance relationships between alleles:
complete, incomplete, and codominance.
Pleiotropic
gene that influences many traits.
An individual’s phenotype is often as much a product of
the environment as it is a product of the genotype.
Gene-by-environment interaction
combined effect of genes and environment.
When gene-by-gene interaction occurs
one trait is influenced by the alleles of two or more different genes.
Discrete traits
traits that are clearly different from each other.
Quantitative traits
continuously varying traits that don’t fall into discrete categories.
Quantitative traits share a common characteristic:
when the frequencies of different trait values observed in a population are plotted on a histogram, or frequency distribution, they often form a bell-shaped curve, or normal distribution.
Nilsson-Ehle
if many genes each contribute a small amount to the value of a quantitative trait, then a normal distribution results for the population as a whole.
Polygenic inheritance of quantitative traits
many genes are involved in specifying traits that exhibit continuous variation.
Mode of transmission
describes a trait as autosomal or sex-linked and gives the type of dominance of the allele.
